Re: LF: W1VD amp help - more waveforms

[N1BUG <paul@n1bug.com>]

Jay,

I have no reliable way to measure capacitance. The ones I used
originally were NOS Sangamo caps. The physical dimensions are the
same as I find listed for DM19 caps. Last night I swapped one out
for a CDE of same length and height but thicker. Zero measurable
change in ringing. I put squares of thin shim stock under the
grounded lead of each snubber resistor so that now lead length is
basically zero. Absolutely no measurable change in ringing.

I was just curious whether the fact that changing cap values has an
affect might point us toward something we're somehow missing.

I will find some of the Russian mica caps for a try at some point.

Meanwhile I'll find some smaller lamp cord and try once more.  To be
honest I'm not at all convinced my secondary winding is tight enough
either. In places it can be manipulated a bit while the amp is
operating at low power. Doing so makes an easily observable change
in the ringing. If there is a technique for getting that first
winding any tighter, it's one I haven't yet learned!

Paul



On 04/10/2018 06:25 AM, jrusgrove@comcast.net wrote:
> Paul
>  
> Okay on 78 material.
>  
> Wonder if you measured your snubber caps? Notice they're maroon
> color which would indicate they're old ... possibly used or an off
> brand? All new CDE mica caps have been yellow in color for some
> time.  Can't tell from the pix ... are they really DM19 size?  The
> russian blue glass mica's that Chris mentioned (same as I used) are
> excellent. I've used these in applications where other 'lesser'
> mica's were pushed beyond their limits. Will check to see if I have
> a couple extra. Don't be in a hurry to start changing values since a
> number of these amps have been built 'to spec' with the no ringing
> problem. There's something in your amplifier / system thats causing
> the anomoly.
>  
> Did you try using a wider connection to ground on the snubber
> resistor? Grab some zip cord off a little used lamp ... it will be
> fine for 'low power' testing. It will wind tight aagainst the core.
>  
> Jay W1VD
>  
>       
>  
>  
> 
>     *----- Original Message -----*
>     *From:* N1BUG <paul@n1bug.com <mailto:paul@n1bug.com>>
>     *Reply-To:* <rsgb_lf_group@blacksheep.org
>     <mailto:rsgb_lf_group@blacksheep.org>>
>     *To:* <rsgb_lf_group@blacksheep.org
>     <mailto:rsgb_lf_group@blacksheep.org>>
>     *Sent:* 4/9/2018 9:37:37 PM
>     *Subject:* Re: LF: W1VD amp help - more waveforms
>     --------------------------------------------------------------------
>     The core is 78 material.
> 
>     I tried again with different wire. The winding is somewhat tighter
>     on the core but definitely not what I was hoping for. Clearly I am
>     not bringing required skills to the table on constructing this.
> 
>     Drain waveforms became somewhat asymmetrical with one phase having a
>     somewhat different shape from the other but peak voltage was
>     similar... 65V on one side, 63V on the other with 13VDC supply.
> 
>     I'm sure this was a bad idea but out of curiosity I tried adding
>     another 500 pf in parallel with the 1500 pf snubber cap on one side
>     only. Power output and efficiency did not change but peak voltage on
>     that side dropped a couple of volts. I then increased that side to a
>     total of 3000 pf. Power output and efficiency has still not changed
>     at all but peak voltage on that side is down to 50V and it stops
>     ringing significantly sooner than the other side. Does this suggest
>     anything other than insanity of the builder?
> 
>     Paul
> 
> 
> 
>     On 04/09/2018 05:29 PM, jrusgrove@comcast.net
>     <mailto:jrusgrove@comcast.net> wrote:
>     > Paul
>     >
>     > Maybe try some 14 or 16 gauge lamp cord ... it's pretty
>     pliable and can be wound tight against the
>     > core. That's what I used in the 500 watt deck. Put a piece of
>     wet paper towel around the insulation
>     > when soldering to prevent 'melt back'.
>     >
>     > Is your core 77 or 78 material?
>     >
>     > On your driver board ... are there reasonably wide traces ...
>     especially from the 12 volt power
>     > supply to the IR2110? Peak currents can be high driving the
>     gate C. Is the 12 volt supply reasonably
>     > stout?
>     >
>     > Jay W1VD
>